The present invention relates to layered heat exchangers, for example, for use as evaporators for motor vehicle air conditioners.
Layered heat exchangers made of aluminum and adapted, for example, for use as evaporators for motor vehicle air conditioners generally have a heat exchange portion for subjecting the refrigerant flowing through a refrigerant channel and the air flowing outside the refrigerant channel to heat exchange. The heat exchange portion is provided by a required number of aluminum intermediate plates arranged in superposed layers, and a pair of end plates positioned respectively at opposite ends the assembly of the intermediate plates in the direction of superposition thereof. Conventionally, a pipe mount plate is brazed to the upper portion of outer surface of the end plate at one end of the heat exchange portion, two pipe sockets arranged side by side at front and rear are provided on the mount plate, and a refrigerant introduction pipe and a refrigerant discharge pipe are inserted into the respective sockets for connection.
The intermediate plates, the opposite end plates and the pipe mount plate of the heat exchange portion are brazed in a furnace as by the vacuum brazing method or flux brazing method.
However, in the case of such a furnace brazing method which is practiced in a nitrogen gas atmosphere, faulty brazing (faulty joint) will result unless air is replaced with nitrogen gas. When the pipe mount plate provided with the front and rear two pipe sockets described is brazed to the end plate in the furnace, a fault is liable to occur in the brazed joint between the pipe mount plate and the end plate at the intermediate portion of the mount plate between the two pipe sockets. If such a faulty brazed joint is produced, the refrigerant introduction channel communicates with the refrigerant discharge channel through the faulty joint, forming a so-called shortcut channel at the intermediate portion and giving rise to the problem of internal leakage of the refrigerant.
To overcome this problem, accordingly, it has already been proposed to form a slit 35 in a pipe mount plate 32 at an intermediate position between a refrigerant introduction pipe socket 33 and a refrigerant discharge pipe socket 34 on the plate 32 as shown in FIG. 5 (see, for example, JP-A No. 9-170892). With the layered heat exchanger thus proposed, the pipe mount plate 32 and an end plate 31 are brazed to each other when the heat exchange portion is collectively brazed. Should a fault occur in the brazed joint between the end plate 31 and the mount plate 32 at the intermediate portion of the mount plate 32 between the front and rear two pipe sockets 33, 34 to create a shortcut channel, the presence of the slit 35 will open the shortcut channel to the outside at the portion of the slit 35. When the heat exchanger assembled is checked for fluid leakage, the fluid flowing through the shortcut channel invariably leaks out through the slit 35, whereby the internal fluid leakage can be detected properly to prevent the shipment of faulty products due to internal leakage.
However, in the case where the slit 35 is formed in the pipe mount plate 32 between the front and rear two pipe sockets 33, 34, a portion 36 of the plate under the slit 35 (indicated by chain lines in FIG. 5) is liable to become depleted of the brazing material. The depletion of the brazing material entails the likelihood of developing a shortcut channel. Furthermore, the brazed joint between the end plate 31 and the pipe mount plate 32 is prone to become incomplete at the edge portions defining the slit 35, similarly entailing the problem that a shortcut channel is very likely to develop.
We have conducted intensive research in view of the foregoing problems and found that the faulty brazed joint in the slit-defining edge portions of the pipe mount plate 32 is attributable to the presence of air remaining unremoved during brazing from the clearance of the slit 35 in the plate 32 as held between the outer surface of upper end of the end plate 31 and a jig on the same side, when a required number of intermediate plates (not shown), opposite end plates 31 and pipe mount plate 32 are assembled in layers, then held at the opposite sides of the assembly from outside using the jig like the one disclosed, for example, in JP-A No. 4-22571 and collectively brazed in a furnace as by the vacuum brazing method or flux brazing method for the fabrication of a heat exchange portion. More specifically, we have found that a complete brazed joint can not be formed owing to oxidation with the oxygen contained in the remaining air, consequently producing a faulty joint between the end plate 31 and the pipe mount plate 32 at the slit-defining edge portions.
We have found that when the components of the heat exchange portion are held assembled by a jig and heated in a furnace for collective brazing, such a situation is avoidable by allowing air to flow out during brazing from the clearance of the slit 35 in the pipe mount plate 32 as held between the outer surface of upper end of the end plate 31 and the jig disposed at the same side, whereby the present invention has been accomplished.
An object of the present invention is to provide a layered heat exchanger which is free of the foregoing problems.
The present invention provides a layered heat exchanger of the type which has a header portion at one side, i.e., a layered heat exchanger wherein an end plate at one of opposite sides of the exchanger is covered over an outer surface of an upper end portion thereof with a pipe mount plate having a fluid introduction pipe socket and a fluid discharge pipe socket arranged side by side respectively at front and rear, the pipe mount plate being brazed to the end plate. The heat exchanger is characterized in that the pipe mount plate has a cutout positioned between the fluid introduction pipe socket and the fluid discharge pipe socket, the cutout having a lower end left open downward at a lower end of the mount plate or an upper end left open upward at an upper end of the mount plate.
In fabricating this layered heat exchanger by assembling a required number of intermediate plates and opposite side end plates in superposed layers, with a pipe mount plate fitted over the outer surface of upper end portion of the end plate at one side, holding all of these components by a jig at opposite sides of the assembly from outside and heating the resulting assembly in this state in a furnace for collective brazing as by the vacuum brazing method or flux brazing method, air is allowed to flow out of the clearance of the cutout in the pipe mount plate as held between the upper-end outer surface of the end plate and the jig on the same side, via the open upper or lower end of the cutout. The air can therefore be removed effectively to ensure brazing, forming satisfactory fillets at the cutout edge portions to produce a reliable brazed joint between the end plate and the pipe mount plate, hence greatly improved brazability. Accordingly, the occurrence of a shortcut channel between the refrigerant introduction channel and the refrigerant discharge channel due to faulty brazing can be prevented more reliably.
The layered heat exchanger of the present invention is further characterized in that the cutout has an upper end extending upward to a level beyond an upper end of the fluid introduction pipe socket and an upper end of the fluid discharge pipe socket and has its lower end left open downward at the lower end of the mount plate, or has its upper end left open upward at the upper end of the mount plate and has a lower end extending downward to a level below a lower end of the fluid introduction pipe socket and a lower end of the fluid discharge pipe socket.
The heat exchanger is free of the likelihood that a shortcut channel will occur between the two pipe sockets.
Should a faulty brazed joint be formed between the end plate and the pipe mount plate to develop a shortcut channel, the presence of the cutout in the pipe mount plate reveals a liquid leak when the heat exchanger assembled is checked for fluid leakage, enabling the inspector to recognize the fault from outside easily for the reliable detection of the internal fluid leakage. The shipment of faulty products due to internal leakage is therefore avoidable.
The present invention will be described in greater detail with reference to the accompanying drawings.